Pre-Stack Seismic Data Analysis with 3D Visualization A Case Study*

Transcription

1 Pre-Stack Seismic Data Analysis with 3D Visualization A Case Study* Yongyi Li 1, Josh Feng 1, and Maggie Jiao 1 Search and Discovery Article #41546 (2015)** Posted February 16, 2015 *Adapted from extended abstract prepared in conjunction with a presentation given at CSPG/CSEG 2007 GeoConvention, Calgary, AB, Canada, May 14-17, 2007, CSPG/CSEG/Datapages Paradigm Geophysical, Calgary, AB, Canada (yli@paradigmgeo.com) Abstract The dataset generated in pre-stack seismic processing consists of a variety of attributes and CMP gathers. It poses challenges in the quick evaluation for reservoir characterization and often prevents the full exploitation of valuable information contained in pre-stack seismic data. We present a case study to demonstrate how to improve interpretation of a 3D survey by using traditional approaches and new techniques in 3D visualization. Introduction The interpretation of 3D pre-stack seismic data involves post-stack and pre-stack seismic attribute volumes, CMP (or CIP) gathers, and well log data. The size of the dataset is commonly large. In order to conduct pre-stack data interpretation efficiently for an optimized solution in reservoir characterization, one not only needs to have knowledge on how to analyze pre-stack seismic data, but also needs new technologies for visualization. In this study, we use a 3D dataset to demonstrate how to efficiently conduct the interpretation on pre-stack seismic data with advanced 3D visualization tools. The study area is located in Southern Alberta, with a multi-channel system in the target formation. Figure 1 shows the base map with the horizon across the base of the target zone. The well logs from three wells are shown in Figure 2. The target zone is the Ellerslie sand, which has lower velocity and density in comparison to the encasing shale. The velocity of the sand is between 3600 m/s to 4000 m/s. In well A, the encasing shale has similar rock properties. In well B, only part of the Ellerslie Formation was drilled. And in well C, the shale above has similar velocity as the sand, and a high velocity layer exists at the base of the Ellerslie Formation. Pre-stack time migration was conducted in this study. AVO processing was then performed and various attributes were generated (Table 1). Figure 3 shows the well ties to the PSTM sections. In general, the well ties are good.

2 Figure 4 shows the 3D displays of the channel system from the PSTM volume. The amplitude in blue is the trough corresponding to the top of the channel system. We see that there is little differentiation in amplitude between the three locations and even the thickness and the reservoir quality are significantly different. To explore the possibilities of whether the reservoir quality can be distinguished we examined P- and S-impedances, Lambda*rho, Mu*rho as well as Vp/Vs ratio. Figure 5 shows inline and crossline sections corresponding to the location of well A. It can be seen that the channel is well defined by the P-impedance. 3D displays show that well B has relatively higher values in P-impedance and especially in S-impedance (Figure 6). They also show that well A has the lowest Vp/Vs ratio. 3D Visualization of Attributes with Gathers We present a method to analyze CMP gathers using a pseudo 3D formed by CMP gathers in which crossline is the offset. The pseudo 3D can be displayed with post-stack or pre-stack attributes. One of the advantages of this method is that the amplitude versus offset at a given event can be viewed with a horizon that has constant time in the crossline direction. Figure 7 shows the base map with the original 3D and two pseudo 3Ds corresponding to the inlines and crosslines of the well A. Figure 8 gives an example of 3D visualization of a pseudo 3D. The characters of amplitude versus offset along the line can be identified. Conclusions A 3D case study has been presented to demonstrate the use of traditional approaches with 3D visualization. A new 3D visualization technique has been proposed to view and analyze seismic attributes and CMP gathers simultaneously. This technique uses the pseudo-3ds formed by CMP gathers using offset as crossline. Acknowledgments The authors would like to acknowledge Devon Energy Canada for permission to use this dataset. The authors would also like to thank Paradigm Geophysical Canada for its support.

3 Figure 1. Base map of the study area.

4 Figure 2. Well logs used in this study.

5 Figure 3. Well ties to inline sections across the three well locations.

6 Figure 4. PSTM display with a flattened horizon across the channel system.

7 Figure 5. Well ties to inverted P-impedance at the location of well A: (a) Inline section, (b) Crossline section, (c) and (d) Zoomed inline and crossline sections at the target zone.

8 Figure 6. (a) P-impedance, (b) S-impedance, (c) Lambda*rho, and (d) Vp/Vs ratio.

9 Figure 7. Base map of original 3D with pseudo 3Ds.

10 Figure 8. 3D visualization of a pseudo 3D.

11 Table 1. Seismic attributes generated from pre-stack seismic processing.